Multicamera calibration using `ds-none` model fails

[frneer]

Calibration of cameras using the ds-none fails.

Command

rosrun kalibr kalibr_calibrate_cameras --target /data/board.yaml --no-outliers-removal --no-final-filtering  --bag /data/ros1.bag --models ds-none --topics /BFS_25037059/image 

Error log

importing libraries
Unable to init server: Could not connect: Connection refused
Unable to init server: Could not connect: Connection refused

(kalibr_calibrate_cameras:1070): Gdk-CRITICAL **: 18:11:16.680: gdk_cursor_new_for_display: assertion 'GDK_IS_DISPLAY (display)' failed
Initializing cam0:
	Camera model:	  ds-none
	Dataset:          /data/ros1.bag
	Topic:            /BFS_25037059/image
	Number of images: 12058
Extracting calibration target corners
  Extracted corners for 4563 images (of 12058 images)                              
Traceback (most recent call last):
  File "/catkin_ws/devel/.private/kalibr/lib/kalibr/kalibr_calibrate_cameras", line 15, in <module>
    exec(compile(fh.read(), python_script, 'exec'), context)
  File "/catkin_ws/src/kalibr/aslam_offline_calibration/kalibr/python/kalibr_calibrate_cameras", line 465, in <module>
    main()
  File "/catkin_ws/src/kalibr/aslam_offline_calibration/kalibr/python/kalibr_calibrate_cameras", line 188, in main
    if not cam.initGeometryFromObservations(observations):
  File "/catkin_ws/src/kalibr/aslam_offline_calibration/kalibr/python/kalibr_camera_calibration/CameraCalibrator.py", line 57, in initGeometryFromObservations
    success = self.geometry.initializeIntrinsics(observations)
RuntimeError: OpenCV(4.2.0) ../modules/calib3d/src/calibration.cpp:1171: error: (-2:Unspecified error) in function 'void cvFindExtrinsicCameraParams2(const CvMat*, const CvMat*, const CvMat*, const CvMat*, CvMat*, CvMat*, int)'
> DLT algorithm needs at least 6 points for pose estimation from 3D-2D point correspondences. (expected: 'count >= 6'), where
>     'count' is 4
> must be greater than or equal to
>     '6' is 6

Similar issue in original kalibr ethz-asl#555

[frneer]

Allegedly this PR includes a patch for this issue: ethz-asl#757

I'm going to give it a shot.